Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to and, in particular, to improvements in the methods and apparatus for using a rebound spring carried on a shock absorber that is intended to utilize the unsprung weight of the wheel/axle system during rebound. More particularly, it is to resist rollover, sway, yaw and other chassis motion.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In the past ten years the numbers of sport utility vehicles xe2x80x9cSUVxe2x80x9d and pickup trucks have increased dramatically to the point where those vehicles are more popular than the millions of passenger cars on the road. The SUV and trucks inherently have a higher center of gravity (CG) than normal passenger cars due to the need for higher ground clearance for bad weather travel (snow and ice), off-road use and/or for pickup truck payloads. Vehicles with a higher CG have a greater propensity to sway or even rollover during abrupt lane changes and evasive steering maneuvers than the lower normal passenger cars.
One important arrangement of all these vehicles is the method of suspension used. Except for the use of hydraulic shock absorber damping resistance to rebound, all vehicle chassis and body loads are supported on the vehicle axles with various types of suspensions that have springs that resist primarily load and jounce of each wheel axle. No existing suspensions using coil springs, load leaf springs, air springs, torsion bars or rubber blocks suspensions have any other provision for rebound control of the forces due to inertia or gravity type negative suspension loads. Particularly, those rebound forces occurring at the inside wheel during hard cornering or if a wheel drops into a pothole.
Typically, changes in suspension loads while driving straight along a road are caused generally by reactions to bumps, potholes, and roughness encountered by the vehicle wheels during their interaction with the road surface. Thus the suspension springs and associated shock absorbers quell the harshness and movements being transmitted to the body/chassis.
The sway or side to side rolling motions that vehicles experience due to cornering forces, also cause vehicle springs to be loaded or unloaded, depending which way the vehicle is rolling during cornering. Many vehicles have an anti-sway/roll bar installed to help the vehicle body resist the rolling actions. These devices help the vehicle partially resist roll but only as it relates to the body lean, because they are fixed to the sprung mass and leaning with the body. Thus, they can actually reduce the load on the unloaded side of the vehicle. They use the body as a structure to support the torsion bar of the anti sway system transferring wheel jounce motion across to the opposite side. The disclosure herein will obviate the need for anti-sway bars, saving the cost of providing and installing them. Shock absorbers only dampen the bouncing movement of the vehicle wheels and suspension caused by the reaction to road surface, cornering and braking. Thus, the rate of sway may be affected only to a minor degree.
A floating aluminum piston is placed between the fluid moving piston and the end of the shock body. The floating piston has nitrogen gas behind it that is at a preset pressure. This piston is used in racing shocks and other lift type shocks to do two things, first to pressurize the fluid at all times and second to raise the vehicle ride height. It is not practical to fill the entire shock body with fluid on both sides of the fluid piston. This ensures that as the fluid moving piston moves away from the end of the cavity as it would during extension or xe2x80x9creboundxe2x80x9d travel, it does not permit a vacuum to form behind the fluid piston and sucking against the shock travel. It maintains a pressure front against the fluid to ensure that it is induced to pass the fluid piston during jounce travel. The fluid piston has holes in it to allow the fluid to pass by it and flexible shims on both sides of the fluid piston are adjusted in strength to set the resistance to flow through the piston during normal movement. Stiffer shims result in higher resistance to the fluid being compressed against them.
All this and the use of nitrogen pressure against the piston are typical of existing shock absorber design. The basic tubular shock absorber is well known to skilled artisans, and is a commodity and is disclosed in numerous patents. The typical shock absorber is designed to dampen motion and with coil over springs adjust the ride height and/or spring stiffness.
U.S. Pat. No. 2,160,541 has a paired spring suspension connected in series to only support load and jounce with the added spring coupled in line with the main spring for increasing the effective spring constant at the extremes of suspension travel. The techniques disclosed in the various embodiments of ""541 are in the nature of an overload spring that engages and changes the spring constant at the extremes of wheel travel. There is no spring in ""541 connected to specifically resist rebound forces due to diverging motion of the sprung weight to unsprung weight. The disclosure of ""541 specifically states that the higher spring constant results in less flex (on page 2 column 1 at lines 6 to 8), xe2x80x9c . . . which opposes any tendency of the vehicle to overturn laterally when negotiating a curve.xe2x80x9d In each embodiment of ""541 the springs act in unison to control primarily load and jounce and there is no teaching of a particular connection to directly apply rebound reaction of unsprung weight to one of the springs. The graph in ""541 showing wheel travel verses spring forces verifies these conclusions. U.S. Pat. No. 5,263,695 discloses a refinement of the ""541 teaching that includes a shock absorber for damping motion and an elastic block to ameliorate the transition between first and second springs for carrying the load. In addition to many disclosures in ""695 of prior paired spring configurations there is a specific explanation in column 5, lines 1 through 5 as follows:
xe2x80x9cThe suspension according to the invention produces a comfort level which is higher the more the transition from one stiffness to the other takes place progressively (see the patents cited in the state of the art).xe2x80x9d
The state of the art referred to includes prior patents of the same inventor and the acknowledgements of those prior patents clearly identifies the teachings as merely two springs of different stiffness in series. Even in FIG. 7 of ""695 the springs are concentrically mounted but act in series, see column 4, lines 8 through 12. At best the structures for multiple springs shown in these patents have differing spring rates to give an allegedly more comfortable ride but do not specifically disclose rebound control.
U.S. Pat. No. 3,830,517 is a motorcycle rear wheel spring suspension wherein a top spring is longer and absorbs upward road shock and a bottom spring absorbs the rider""s weight. Nothing is disclosed about resisting rebound with either the top or bottom spring and no attachment of the springs is shown or described that would operate to control rebound of the sprung weight.
U.S. Pat. No. 3,049,359 has a pair of coaxial coil springs designed to maintain ride height by automatic screw adjustment of the smaller and lighter inner tension coil spring. No disclosure of rebound control of sprung weight is made and the inner tension coil spring loadings are varied only in so far as the ride height is less or more than required as such the size and strength of the inner tension spring would be insufficient to transfer the unsprung weight to the chassis and resist rebound. Moreover the working travel of both springs appears to be the same; thus, no rebound control is possible.
No existing suspension system suspends the chassis and/or body between opposing springs to counter load and jounce and reaction and rebound along different portions of the axle and wheel travel. An opposing spring suspension as disclosed herein can have little effect on the ride stiffness, but stabilizes cornering and evasive maneuvering sway by utilizing the unsprung weight of the axle system thus helping the vehicle to resist roll while maintaining the general ride quality.
U.S. Pat. No. 3,297,312 has a combination shock absorber and spring for automobile suspensions. Close examination reveals that a main rod connects between a top cap and a nut to bottom tube. It appears that the rod will bottom out against the tube end when the springs are compressed because rod 52 is of set length and incompressible. The four springs stacked, as a unit, abut each other to act as one continuous variable rate spring. Specifically, the upper two springs have a disc that separates them that shifts up and down with the movement of the springs. The disc has valve holes in it to permit the movement of fluid to each side of the disc to act as a shock absorber. This appears to have minimal effect or use.
U.S. Pat. No. 5,183,285 has a suspension of a stiffness that is greater between the operating load position and the suspended wheels position than between the operating load position and the collapsed position. It is a suspension and a suspension process that uses a greater stiffness in the region of xe2x80x9creboundxe2x80x9d than in the region of xe2x80x9cbumpxe2x80x9d with means for smoothing the stiffness from the passage of one region to the other, and means for varying the reference position for xe2x80x9coperating loadxe2x80x9d as a function of the number of persons and the load in the vehicle. A suspension wherein the stiffness is greater in the region between the position xe2x80x9coperating loadxe2x80x9d and a position xe2x80x9csuspended wheelsxe2x80x9d than in the range between the position xe2x80x9coperating loadxe2x80x9d and a position xe2x80x9ccollapsed suspensionxe2x80x9d up to shock abutment. The suspension has stiffness greater in the region of xe2x80x9creboundxe2x80x9d than in the region of xe2x80x9cbumpxe2x80x9d; if these are graphically represented, a change of thickness represented by a break in the slope appears. FIGS. 13, 14 and 16 in U.S. Pat. No. 5,183,285 have a rebound spring around a shock positioned by a jack for varying the reference position for xe2x80x9coperating loadxe2x80x9d as a function of the number of persons and the load in the vehicle. The jack varies the preload position so there is no gap between rebound and bump.
U.S. Pat. No. 6,273,441 has a load leaf spring suspension system with an elongated stabilizing spring mounted there above the axle. The added spring communicates roll resistance to the vehicle axle at its top center section. Force is concurrently applied at the ends of the stabilizing spring to the leaf spring of the vehicle by shackles. Adjustment of the device is achieved by use of a plurality of mounting apertures for the shackles located at varying distances from the center of the stabilizing spring thereby allowing for adjustment by the user for desired performance characteristics. Further force adjustment is achieved with one or a combination of an optional axle spacer located at the center section of the stabilizing spring to communicate with the axle. This stabilizer system does not employ opposing spring technology.
An influence is delivered on the vehicle center of gravity by opposing spring. The center of gravity of the unsprung mass relative to the center of gravity of the sprung mass is affected during the cornering maneuvers. Without a tension or opposing spring to xe2x80x9ctetherxe2x80x9d the sprung mass to the unsprung mass the unsprung mass does not initially help resist the movement upwards of the sprung mass. This resistance is best appreciated in a vehicle with very heavy unsprung mass relative to a lighter sprung mass during corn ring versus a vehicle with light unsprung mass relative to a heavy sprung mass. The former is recognized as undesirable and the latter is greatly preferred and sought after in design of vehicles. Often the physical limits of the vehicle components determine the practical boundaries of the sprung weight to unsprung weight ratio. The disclosure herein has an approach to ameliorate the dynamics of that relationship.
U.S. Pat. No. 6,017,044 has as it""s main thrust regulation of spring rebound and bound. Vertical downward jacking-force characteristics of the front suspension is set to be stronger relatively with respect to vertical downward jacking-force characteristics of the rear suspension during cornering. This is achieved by two means. The first is the use of a very strong bump rubber in FIG. 3 of U.S. Pat. No. 6,017,044 that comes into play at the extreme end of the front jounce travel. This bump rubber is not needed in our disclosure. Second, a short xe2x80x9cspringxe2x80x9d item in FIG. 4 of U.S. Pat. No. 6,017,044 is intended to help control xe2x80x9cjack upxe2x80x9d of the rear suspension occurring near the extreme end of the roll. The working distance traveled is very short.
U.S. Pat. No. 6,220,406 discloses a damper for reducing sway. It discloses background on various types of shock absorbers used in connection with motor vehicle suspension systems to absorb unwanted vibrations that occur during various driving conditions. To dampen the unwanted vibrations, shock absorbers are generally connected between the sprung portion (i.e., the vehicle body) and the unsprung portion (i.e., the suspension) of the vehicle. A piston assembly is located within the working chamber of the shock absorber and is connected to the body of the motor vehicle through a piston rod. Generally, the piston assembly includes a primary valve arranged to limit the flow of damping fluid within the working chamber when the shock absorber is compressed or extended. As such, the shock absorber is able to generate a damping force to smooth or dampen the vibrations transmitted from the suspension to the vehicle body. Typically, these vibrations occur from forces generated in a vertical direction between the vehicle body and the driving surface.
The greater the degree to which the flow of damping fluid within the working chamber is restricted across the piston assembly, the greater the damping forces that are generated by the shock absorber. It is also possible to implement a primary valve arrangement that produces one magnitude of damping on the compression stroke, and a second magnitude of damping on the rebound stroke. These different damping rates are typically constant as varying the sizes of the compression and rebound bypass orifices produces them.
While these shock absorbers produce ride comfort levels ranging from xe2x80x9csoftxe2x80x9d to xe2x80x9cfirm,xe2x80x9d few, if any, of the known shock absorbers produce varying degrees of damping in a passive manner. The shock absorber systems in use are capable of producing varying degrees of damping force; typically achieve this through the use of active control systems. These systems generally react to the vertically generated forces placed upon the vehicle suspension.
Accordingly, in ""406 a shock absorber that includes a primary damping mechanism for counteracting the vertical forces placed upon the vehicle, and a secondary damping mechanism which is capable of providing varying damping in response to horizontal and lateral forces that are placed upon the vehicle suspension. Secondary and variable damping is provided in proportion to the lateral force encountered by a passive control or valves arranged to implement a passive anti-roll system for enhancing the control to the vehicle provided by the vehicle suspension. While such a passive damping system also eliminates the need for complicated and expensive controls to actively provide the varying degrees of damping, it is not easily adapted to the large variety of vehicles and their suspensions.
The problem of the lateral forces placed upon the vehicle suspension is they are generated during high-speed cornering. As the suspension and tires counteract these lateral forces, a rolling action on the vehicle body is produced. When these rolling forces exceed the limit for the vehicle, a rollover condition may be created wherein the vehicle is literally flipped over on its side. Accordingly, it is desirable to provide a shock absorber that provides increased resistance in response to these lateral and horizontal forces for counteracting or at least minimizing these rolling forces and the lift associated therewith.
In the disclosed device and method, a rebound spring is placed to resist the lengthening of the shock absorber from a position that starts one inch into jounce travel from normal ride height to the full rebound suspension travel position. This rebound spring is opposing and resisting the forces that are generated when the suspension is unloading as for example during cornering. Namely the forces caused by the vehicle suspension spring trying to return to its free position and the centrifugal forces naturally resulting during cornering.
Using an additional coil spring mounted about the shock absorber to resist the rebound motion of the sprung weight applied by movement thereof away from the design height reduces chassis roll. The shock absorber thus reduces the initiation of rebound travel between the sprung and unsprung weights as the vehicle becomes lighter due to dynamic forces inducing roll or lift of the chassis and vehicle body.
The transitory effects of body roll during cornering flex the load springs on the side of the vehicle following the outside of the turn due to increased transfer weight to that side. Meanwhile the springs on the side of the vehicle, following the inside of the turn, unload extending toward their free position using the axle as a location for inducing lift of the sprung weight on that side resulting in increased body roll. Roll or sway during sudden cornering or evasive maneuvers rotates the vehicle and its center of gravity xe2x80x9cCGxe2x80x9d around the Roll Center axis.
The Roll Center axis is a function of the particular vehicle""s suspension geometry. Roll or sway is increased if the vehicle center of gravity is raised as in a SUV, four-wheel drive vehicle or truck. A sudden turn opposite the direction of vehicle travel can cause momentum to continue the sway of the vehicle forcing its center of gravity to move laterally past its maximum upright position, and so the vehicle continues on rolling and overturns.
The solution, as disclosed herein, may include an added rebound spring mounted coaxial about the shock absorber tube to act primarily to resist rebound of the suspension from the design height position and thereby apply resistive force to the chassis via the shock absorber to reduce lift. The coil rebound spring can also be added to a strut type suspension for exactly the same purpose. It is an advantage of the present invention that it can be easily and inexpensively added as an after market supplement to either the front or rear of an existing vehicle suspension with tubular shock absorbers. It is a further advantage of the present invention that the coil rebound spring has very little influence on ride height and/or ride stiffness.
The coil rebound spring works from one inch of jounce travel all the way to full rebound travel of the shock absorber. It works to prevent the onset of roll from the design height, rather than limiting the roll to a certain amount after it has rolled a certain amount. Limiting the roll from the design height position serves to reduce the momentum or inertial weight gain that occurs at the initiation of roll and continues after roll has begun. In other words, we seek to eliminate as much roll as possible from the outset. Rebound control overlaps the jounce control; therefore the disclosed system is truly bi-linear, a preferred embodiment.